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JunosE 11.3.x Multicast Routing Configuration Guide
Figure 21: Source-Rooted Tree
PIM Sparse Mode
212
SSM is an extension to the Any Source Multicast (ASM) service model and facilitates
the deployment of broadcast (one-to-many) applications, such as Internet TV and radio
where large receiver audiences require traffic from a few well-known sources.
Figure 21 on page 212 represents how PIM builds an (S,G) entry in an SRT. When multiple
routers are connected to a multiaccess network, one router is assigned the role of the
designated router. The designated router receives data from the source on interface 1/0
and multicasts the data to its downstream neighbors on interfaces 1/1, 2/0, and 2/1. In
the designated router routing table, the entry for this operation lists the source as the IP
address of the source and the group as the IP address of the multicast group.
Neighbors exchange hello messages periodically to determine the designated router.
The router with the highest network layer address becomes the designated router. If the
designated router subsequently receives a hello message from a neighbor with a higher
network layer address, that neighbor becomes the designated router.
In addition to the features PIM sparse mode supports for IPv4, this IPv6 implementation
of PIM sparse mode also supports remote neighbors.
For a description of PIM sparse mode, see "Configuring PIM for IPv4 Multicast" on page 79.
Joining Groups
A host's designated router (DR) sends join messages to the RP when that host wants to
join a group. When a host wants to leave a group, it communicates with its designated
router through MLD. When the designated router no longer has any hosts that belong to
a particular group, it sends a prune message to the RP.
Timers
PIM sparse mode uses timers to maintain the networking trees.
Copyright © 2010, Juniper Networks, Inc.
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